The use of EC array probes for NDT/NDI is well known in existing practice. Generally, an EC array probe comprises a multiplicity of individual EC sensors, each individual EC sensor comprising eddy current coils. Some of the coils are configured as driver coils, creating a variable magnetic field in a test object, while other coils are configured as sensing coils which detect magnetic fields generated by eddy currents in the test object. In some embodiments, the same coil can simultaneously serve both driver and sensing functions. Each individual EC sensor has a center point where there is maximum sensitivity to eddy currents, and therefore maximum sensitivity for detection of defects. This center point is hereinafter referred to as the center of a physical channel of the individual EC sensor. In operation, the EC array probe is scanned near the surface of the test object, and each individual EC sensor is most sensitive to defects in an inspection channel represented by the trajectory path of the center point of the physical channel.
A common problem in EC array testing is the signal amplitude variation due to the limited channel coverage of each probe. The variation, usually referred to as “coverage loss”, is caused by reduction in sensitivity to defects which are not directly under the center point of any sensor, but are located in the space between adjacent sensors where sensitivity is reduced. Consequently the received signal from a given defect, particularly a defect oriented parallel to the direction of motion of the array, will depend on the location of the defect relative to the individual EC sensors.
U.S. Pat. No. 8,125,219 by Jungbluth et al discloses synthetic crack signals which may be positioned between channels in order to reduce coverage loss. However, the interpretation of such signals is based on very specific knowledge of the flaw, and no method is disclosed for creating intermediate virtual channels whose generation is based solely on the physical properties of the coils with no a priori knowledge of the defect being required.
Therefore there exists a need for a general method to reduce the signal variability due to coverage loss, and thereby to enhance the probe resolution and provide better defect imaging.